Track circuit for railway signaling systems



NOV. 8, 1938. Q s. HELD 2,135,497

TRACK CIRCUIT FOR RAILWAY SIGNALING SYSTEMS Filed April 28, 1934 3 Sheets-Sheet l FIG. 1.

INVEN ATTORNEY Nov. 8, 1938. Q s HELD 2,135,497

'TRACK CIRCUIT FOR RAILWAY SIGNALING SYSTEMS Filed April 28, 1934 3 Sheets-Sheet 2"l nas ATTORNEY NOV., 8, 1938. y o, sA HELD 2,135,497

TRACK CIRCUIT FOR RAILWAY SIGNALIING SYSTEMS File@ April 28, 1934 5 Shees-Sheet 3 FIG ATTORNEY Patented Nov. 8, y1938 .UNITED STATES PATENT OFFICE TRACK CIRCUIT Foa-RAILWAY SIGNALING sYs TEMs Oscars. Field, Rochester, Y., assigner to General Railway Signal Company, Rochester v Application' April 2s, uns,l serial No. '122,934 3o clama (ol. zkt- 41) tion Ser. No. 703,775 .mod December 23, 1933,

now abandoned in favor ot lthis application.

A normally energilod track circuit includes a relay energized when the track section is unoccupied by current flowing through the track rails in series, and it is necessary to adjustthis normal energizing current in the track relay to a comparatively low value in order to permit a train occupying the track section to divert suilicient current through the wheels and axles shunting the track rails to reduce this energizing current in the track relay to a degree so as to release its armature. The ballast used between the rails of such a track circuit permits a certain amount of leakage current which affects the track circuit in the same. manner as a train shunt, but to a lesser fdegree. This leakagecurrent however is notA cfa constant. vvalue but varies in accordance with the amount of moisture `present in the ballast, and consequently the track circuit current must at times be regulated to compensate for natural changes inballast condition' in order to maintain a current value in the track relay which permits reliable operation.

In'view ci the above and other considerations, it is proposed in accordance with the present invention to provide means automatically operable to' maintain a constant current in a track relay regardless of changes in values of leakage current through the ballast from one rail to the other, but to permit a change in current in the track .relay which is effected by the entrance of a train into the associated track section. In other words, it is proposed to provide a means which automatically distinguishes between the changes in current resulting from diiferent causes in a manner to maintain a predetermined current in a track relay regardless of various changes in ballast leakage current, but to allow the current in the track relay to change in response to the application or removal of a train shunt upon the track section. It is further proposed to supplement this means for distinguishing between different current changes by a locking means operable to prevent a change in the condition of such a current regulating means I conventioxial insulatedI track section.

throughout the time in which a train is occupying the associated track section.

Other objects, purposes and characteristic features of the invention will be obvious as the description thereof progresses, during which references will be made to the accompanying drawings, which diagrammatically show the invention ina manner to make it easily understood,

ratherthan with the view of showing the particular ,construction preferably employed in practice, and in which:-

Fig. 1 shows in a diagrammatic and conventional manner a preferred form of the present invention as applied to a conventional track circuit. l

Fig. 2 is an enlarged sectional view of a portion of the device shown in Fig. 1..

Fig. 3 shows a modified form of the present invention and also as applied in another manner to a track circuit.

Fig. 4 shows in-.a diagrammatic manner another modified form o1 the present invention and also applied in still another manner to a track circuit.

' of railway track rails l is shown divided from the adjacent track by insulated joints 6 to form a A vtrack relay TR. of the type usually employed to controlblock signals (such as signal S) is `iihown connected across the left hand end of this track section to be normally energized from a suitable source. of energy, such as a storage battery B provided at the right handend of this track section. l A means for automatically varying the amount of resistance included in series with the battery B is shown in Fig. 1 as an electro-magnetic actuating means which may be of substantially the same construction as shown and described in Patent No. 1,835,150 granted to O. S. Field, December 8,1931.

yThis electro-magnetic operating means is shown -in perspective in Fig. 1 as comprising two pole pieces l and 9 constructed of suitable magnetic material and shaped as shown to provide two vertical pole surfaces.y The lower ends of these pole pieces I and 9 are suitably xed to oppositeends of a permanent bar magnet Ill to form a magnetic ileld structurein which the two vertical pole surfacesl of the pole piece 8 arey of one polarity and the two verticalpolefaces of marient magnet I0 shown. 55

An amature coacting with this held structure is provided by a cylindrical core II of magnetic material which is rotatably mounted between the two pole pieces l and 9 by suitable bearings not shown. Two sectors I2 and Il of magnetic material are attached to opposite ends of the body portion of core II by clamping nuts I4, and are oppositely positioned on the core II so that various portions of one sector registers with a vertical surface of one pole piece according to the degree of rotation of the core II, while at the same time a corresponding portion of the other sector registers with the opposite vertical surface of the other pole piece.

A winding I5 is placed around the core II and may be supported by an insulating shell I4 which is provided with extending lugs I1 on each end entering notches Il in each of the pole pieces l and 9. This supporting means holds the winding I5 out of physical contact with the core II in order to permit free rotation of the core I I therein. A means for biasing the amature to a definite position is necessary in the present application of this electro-magnetic operating means, and such a means has for convenience been shown as a counter-weight Il attached to the right hand side of the sector I2. It is contemplated that a spiral spring may be used advantageously in biasing this amature arrangement in the place of the counter-weight Il.

The winding Ii is connected directly across the right hand end of the track rails i as is obvious in Fig. l, and is energized in accordance with the interrail potential at that point. This winding I5 is arranged so that the flux produced by energization thereof is of a polarity forming a pole at the sector I2 which is opposite to the magnetic pole produced in the pole piece 9 by the permanent magnet I0, thus tending to produce a counter-clockwise rotation of the core Il when the winding I5 is energized. The counter-weight I l biases the sector I2 toward a position registering with the pole piece I, and in Fig. l, the sector I2 is shown as operated against the biasing eflect of the counter-weight Il to a position approximately midway between its extreme biased and its extreme operated position in accordance with an intermediate degree of energization of the winding IB.

The response of the amature arrangement to an abrupt change in current value in the winding II is retarded in the present application by a `short-circuited metallic sleeve 2l. which effects such retardation in the usual manner by retarding a rapid change in flux within the core I I. It is obvious that various other means may be employed in the present device in order to allow the response of the'armature to a gradual change in current in winding I5, but to prevent an immediate response to an abrupt change.

The electro-magnetic operating means just described is herein employed to actuate a means for varying the resistance of an electrical circuit, and such a. means is shown in Fig. 1 as a substantially square glass tube 22 having a regular longitudnal curvature which is shown as being the same as the shape of the outward edge of the sector I2, and is suitably attached to the outer surface thereof by means not shown in a manner to be rotated by the sector I2. Two triangular strips 23 of insulating material are fitted within the glass tube 22, and each strip is space-wound with a suitable resistance wire 24 as is more clearly shown in Fig. 2. The ends of the resistance wire 24 are brought out at the right-hand end of the glass tube 22, and these ends may be provided with suitable flexible leads for connecting to an external circuit, while the other or lefthand ends of the resistance wire 24 are Joined to l form a closed circuit. or preferably the winding will always be directly beneath the center of the core II, and consequently at various positions of the sector I2, the mercury globule 2l will move within the glass tube 22 to electrically connect or shunt out various left-hand portions of the resistance wire 24. In other words, in Fig. l, as the energization of winding Il is increased to actuate the sector I2 in a counter-clockwise direction. the mercury globule 2l is shifted to a point nearer the left-hand end of the glass tube 22 thereby shunting the resistance wire 24 of the two strips 22 at a point farther from the extending ends to insert more resistance into the external electrical circuit.

It is contemplated that it will be advantageous to evacuate the glass tube 22. or to provide a reduced pressure of an inert gas therdn before sealingtheglalateachendofthetube 22inthe usual manner.

The variable resistor thus formed by the resistance wire 24 and the mercury globule 20 is shown in Fig. 1 as inserted in series with the battery B employed to energize the track circuit shown. A resistor R which is usually employed in track circuits is also shown in series with the battery B, which then forma a normally energized track circuit wherein current supplied by battery B flows through the dxed resistor R., through the variable resistor Just described and through the track rails l in series to normally maintain the track relay TR. energized.

The winding Il, as previously stated, is connected directly across the battery end of the rails l to thereby actuate the variable resistor in accordance with the interrail potential at this point. This interrail potential will obviously be the potential of the battery B minus the sum o1' the potential drops through the fixed resistor R and through a portion of the resistance wire 24 which is not shtmted out of the circuit by the mercury globule 20. Obviously then if the voltage of the battery B is substantially constant, the current in the winding Il will be inversely proportional to the current through the resistor R and the resistance wire 24, which current as may be seen above causes the difference between the potential across the winding Il and the potential of the battery B.

1f the leakage current between the rails l of Pig. 1 now gradually increases due for example to increased moisture in the track ballast, the voltage drop between the source B and the relay TR tends to exceed a value permitting reliable operation of the relay TR. but this increased leakage current also reduces the voltage across winding Ii due to the increased voltage drop through resistor R and the resistance wire 24, thereby reducing the force tending to rotate the sector I2 in a counter-clockwise direction which allows the counter-weight I9 to proportionally actuate thev 3| and 32 with suitable bearings, Shown diagramsector I2 in a clockwise direction. This rotation of the sector I2 in a clockwise direction shifts the globule of mercury 26 to a position within the glass tube 22 which shunts out a greater portion of the resistance wire 24 and results in an increasedvoltage being applied to the trackrails and obviously to .the track relay TR. It is contemplated that the characteristics of the presentl regulator can be so chosen that this increased potential is of a value which is effective at the relay TR to substantially compensate i'or the gradually increased potential drop fromthe source B to the relay TR, and thereby maintain a substantially constant energization of the relay TR regardless of gradual increase inballast leakage current.

It is also'obvious that a converse operation ofl of the resistance wire 24 thereby reducing thek potential applied to the track rails and to the relayfTR. Likewise, it is contemplated thatwhen the regulator is arranged as stated above, this reduction in potential will effect a substantial compensation for the decrease in potential drop be tween the source B and the relay TR caused by the gradual reduction in ballast leakage current.

However, upon entrance of a train into the track section in Fig. 1, the current supplied by the battery B is quickly increased to a value greatly in excess of normal, which results in an increased voltage drop between the battery B and the relay TR, thereby reducing the voltage across the relay TR to a point effective to release its armature.` The voltage drop between the batthe track circuit is delayed by the short-circuited sleeve 2| until after the track relay TR has released its armature. l

This short-circuited sleeve 2| however can act to retard the effect of the decrease in voltage across the winding I5 upon the armature of the regulator for a short period of time only, which time is found to be less than the time in which the train may occupy the track section. In order to prevent variation of the resistance in the track circuit throughout the time in which the track section is occupied, a locking means has been provided which is effective to maintain a previous position Iof the sector vI2 as long as a train causes the track rails of the associated section to be shunted.

A rather simple electro-magnetic locking means has diagrammatically been shown in Fig. l and Fig. 2 as an actuating coil 28 which may be enclosed in an iron casing 29, as shown in Fig. 2, with a solenoid plunger 30 positioned in the center ofthe coil 28 and operable upward by energization thereof. The plunger 30 may be provided with upper and lower extending rods matically as fixed members 23 arranged to permit vertical movement oi the plunger 3U. The extreme upper end of the upper rod 3i is provided with a brake shoe 84 engageable with the lower edge of the sector I2 when the plunger 30 is operated upwardly. The plunger 30 has herein been shown as biased toits lower position by gravity,

although it is obvious that a spring biasing means may be found more desirable in practice.

The actuating coil 28 of the present locking means is connected in multiple with the variable resistor provided by the resistance wire 24 on the sector I2 in Fig. 1, and is thereby energized at all times in accordance with the potential drop across this resistance wire 24. When the track section is unoccupied the resistance inserted into the track circuits by various amounts of the wire 24 varies inversely in proportion to the current flowing through the resistance wire 24, which thereby maintains the potential drop thereacross and the current in coil 28 substantially constant, but the locking mechanism is so arranged that this amount of current in coil`28 does not sumciently attract the plunger 30 to overcome the force of gravity and engage the brake shoe 34 with the edge oi the sector I2.

'Upon entrance of a train into the track section in Fig. 1, the current through the resistance wirev 24 quickly increases as previously stated, and in as much as the regulator does not immediately respond to this rapid increase in current, the sector I2 is not immediately actuated to proportionally decrease the resistance inserted into the track circuit by the resistance wire 24, and the potential drop across the resistance wire 24 and the current in the lock coil 28 is consequently greatly increased.l This increased current in the coil 28 is now eective to operate the plunger 30 upward and engage the brake shoe 34 with the lower edge of the sector thus preventing any further movement thereof, aswell as maintaining this increased energization of its own coil 28 until the track section becomes unoccupied.

It will now be obvious that the regulator shown in Fig. 1 operates to maintain a substantially constant current in ak track relay regardless of gradual'changes in current in the track section with which the relay is associated, and only operates to so regulate the current in the track relay when such changes in track circuit current are oi a gradual nature such as produced by the effect of changes in weather conditionsvupon the balast resistance between the track rails. l

This distinction between the-rate of change of current allows a train shunt, which results in a very rapid change in current ln the track section, to act in the usual manner to drop the track relay. In as much as the present means for distinguishing between the rate of changew in track circuit current'can be effective for a short period of time onlyto at times retard a current regulation which would defeat the lpurpose of the track circuit, such a distinguishing means' is herein supplemented by a locking means which,l is operated during the period of time in whichf anism is placed at the relay end ofjjthe track' different construction in Fig. 3 than in Fig. 1 although the general operation is the same, and it is desired to be understood that this specific construction is equally applicable to the track circuit arrangement in Fig. 1, and vice versa.

The regulator shown in Fig. 3 comprising an actuating coil 35 enclosed by a magnetic casing 36, and actuating a solenoid plunger 31 upward against a biased spring 35. The lower end of the plunger 31 is connected by a rod 55 to a rigid disc 40 which is in turn fixed to the center portion of a flexible diaphragm 4i. The outer edges of the flexible diaphragm 4| are tightly sealed to a base member 4l by a ring 42 suitably clamped thereto; the base member 43 being hollowed having a small space between the lower surface of the diaphragm 4i and the upper surface of the base 43. 'Ihis space beneath the diaphragm 4| isfilled with mercury or other suitable current conducting liquid 44, and a small duct in the base member 43 allows the passage of the mercury 44 from the space beneath the diaphragm 4I through a small hollow in the base 43 which is covered by a smaller diaphragm 5l ilxed at its outer edges to the base member 43 by a suitable ring 5I; which hollow communicates -with a second duct 45 leading to the lower end of an upright insulating-tube 41.

It will now be obvious that the relation of the force exerted on plunger 51 by coil 35 to the cornpression of spring 38 determines the position of the diaphragm 4i which in turn determines the amount of the mercury 44 which is forced through the ducts 45 and 46 to raise the level of the mercury within the insulating tube 41. A carbon resistance rod 48 is sealed within the insulating tube 41 by a suitable cap 49 so that the lower end of the carbon rod 4l will be submersed in the mercury filling the lower end of this tube, and obviously as the level of the mercury within the tube 41 changes due to a change in the position of the diaphragm 4I, various portions of this carbon resistance rod 4I will be submersed, or shorted out, to vary the electrical resistance between the upper cap 4I of the carbon rod-and the mercury within the tube 41.

The locking mechanism in Fig. 3 comprises a rod 52 extending through the center and sealed to the diaphragm 55 with its lower end shaped to form a valve 53, which when operated downwardly closes the end of the duct 45 to thereby prevent the flow of mercury from the duct 45 into the duct 46. An electro-magnetic means for operating the rod 52 is shown by a coil 55 enclosed within an iron casing 5i and coacting with an armature 51 to operate the rod 52 downward against abiaslng spring 55.

The track circuit shown in Fig. 3 is of the well known type in which a series relay SR is employed at the battery end for the purpose of lighting the signals associated with the next track section in advance only when a train enters the track section to increase the current flowing in the series relay SR sufficiently to attract its armature, which is again released by the departure of the train. This track circuit in section T3 may be traced from the battery B1, through the series approach lighting relay SR, through the lower track rail, through the track relay TR1 to the upper terminal of the resistance rod 45, through the portion of the resistance rod 4I which is not shunted by the mercury 44, through the mercury 44 to the base 45, and back to the battery B through the upper rail of the track circuit and the usual fixed resistor R1. The left hand adjacent track section T1 has a similar circuit energizedby battery 1?J through resistor R.2 and series relay SR1, which relay SR1 closes the energizing circuit for signal S1, as indicated diagrammatically by its front contact 55, when track section T:1 is occupied. The wires leading from the regulating and locking means to the track relay and approach relay have been designated a. b, c, d and e, respectively.

'I'he actuating coil 55 of the regulator mechanisrn is connected in multiple with the track relay TR1 as is obvious from the drawings, and consequently thei'orce acting to raise the plunger 31 against the biasing spring Il is in direct proportion to the degree of energization of the track relay TR1. 1f for some reason, such as an increased amount of moisture in the track ballast, the potential across the relay TR1 falls below its normal value, the voltage across the coil 35 also decreases a proportional amount, thereby allowing the biasing spring Il to force the diaphragm 4I downward which results in raising the level of the mercury 44 in the glass tube 41 to shunt out a greater portion of the carbon resistance rod 4l.

This decrease in the length of the carbon rod .4I which is above the mercury 44 obviously decreases the resistance inserted thereby into the track circuit, and if the characteristics of the present regulator are properly chosen, this decreased resistance will be effective to again raise the voltage across the track relay TR1 to its normal value. The converse operation of the regulator in Fig. 3, or that is, its operation to again increase the resistance inserted into the track circuit by the resistance rod 4l in response to an increased voltage at the relay end, is now obvious and will not be described in detail.

However, when a train, in approaching section T1, enters section T1, the current in the series relay SR1 is suillciently increased to attract its amature, and thereby energize the locking winding 55 from the battery Bz over an obvious circuit completed by front contact 51 oi' relay SR1. The energization of winding 35 operates the valve 5I downward closing the end of the duct 45 thus preventing a change in the level of the mercury 44 in the glass tube 41 and consequently preventing a change in resistance inserted in the track circuit by the carbon rod 4I upon the entrance of the train into the track section T. As soon as the train enters section 'P the track relay TR1 drops, and the energizing circuit for winding 55 is maintained closed through a back contact 5I of relay TR1 which is in multiple with the front contact 51 of relay SR1.

It will now be seen that the regulator in Fig. 3 is enective to maintain a substantially constant current in the associated track relay regardless of changes in ballast conditions as long as both its associated track section and the section immediately in the rear thereof are unoccupied. However, in order not to defeat the purpose of the track circuit by allowing the regulator to function in this manner when the section becomes occupied, a locking means is energized by the entrance of an approaching train into the section immediately in the rear, which locking means acts to prevent further regulation of the current in the track relay and permitting normal response of this track relay to the train shunt. In order to maintain this locked up condition of the regulator during the occupancy of the track section associated therewith, the energizing circuit for the locking means is maintained closed by a back contact of the track relay.

In the modified form of the present invention shown in Fig. 3, it is not essential that the regulator, in itself, distinguishes between a change in voltage across the track relay which is due to a train shunt from a change due to a change in ballast leakage current, as the operation of the regulator in response to a decrease in voltage caused by a train shunt is precluded by the energization ot the locking means before the train actually enters the section associated with such track relay. However, inasmuch as it is intended for the regulator mechanism to respond to gradual changes only in the energization oi the track relay, a check on the initial energization of the locking means may be obtained by providing any conventional means which delays f the response of the regulator to abrupt changes in energization. It is contemplated that the response of the regulator in Fig. 3 to abrupt current changes may easily be delayed by reducing the size of the ducts 45 and 46 thereby preventing a rapid flow of mercury therethrough, or of course a means for delaying flux changes may be provided in coil 35 in the same manner as in Fig. 1.

The means for precluding the regulator operation in response to a train shunt in Fig. 3 takes advantage of the conventional series relay employed to approach light wayside signals.

In the form shown in Fig. 4, a usual insulated track section is provided with a track relay 'I'iii normally energized by current flowing through the rails B8 of the track section in series, which current is supplied by the usual track battery B5 with the conventional fixed series resistor R5. A variable resistor VR is included in series with the track relay TR3, and this variable resistor may be of any suitable type but is herein represented as being of the carbon pile type, which asis well known is made up of carbon discs offering a resistance to the flow of current therethrough which varies inversely in accordance with the compression of these discs.

The compression of the disc oi' the variable 'resistor VR is shown as automatically controlled by an actuating coil AC connected in multiple with the relay 'I'R3 to thereby be energized in accordance with then voltage thereacross. The actuating coil AC affects a conventionally arranged magnetic solenoid plunger AP, which is carried by a non-magnetic rod 69. The rod 89 may be supported in any suitable manner to permit free longitudinal movement, such as by flexible strips 10 and 1|, which strips are held stationary at one end with the other end holding opposite extreme ends of the rod 69 as shown.

The rod 69 is forced downwardly by a compression spring 12, the tension o1' which spring is adjustable by a. screw 13 threaded through a stationary member 1I with the lower end oi' the screw 13 engaging a washer 15 holding the upper end of the spring 12. The downward force thus supplied to the rod 69 is transmitted through a compression spring 18 to the top 11 of the variable resistor VR, and inasmuch as the lower member 18 of the variable resistor VR is stationary it will be obvious that, disregarding the action of the plunger AP, the tension of the spring 12 as adjusted by the screw 13 will determine the resistance oi' the carbon pile variable resistor VR.

accordance with the voltage across the relay TR3, I

as previously stated, which current in coil AC operates to raise the actuating plunger AP against the compression springs 12, or to relieve the compression of the carbon pile variable resistor VR. In other words, the resistance between the top 11 and the bottom 18 oi the variable resistor will be varied in raccordance with gradual variations in the voltage across the track relay TR3. The regulator shown in Fig. 4 then obviously operates to maintain a substantially constant current in the track relay TR3 regardless oi gradual voltage changes thereacross in (the same manner as the other embodiments of vthe present invention previously described.

-The locking means' for preventing actuation of the regulator in Fig. 4 during the presence of a train inthe associated track section comprises a locking cpll LC which may be energized from a local source of energy, such as the storage baty tery B@ ordinarily employed to energize the right able with the side of the rod 89 when the actuating plunger LP is attracted, but normally held out ot engagement therewith by the spring 80. It is contemplated that, if necessary, the rod 69 may be provided with peripheral serrations or an abraded surface to offer a better gripping surface to the frlctional braking member 83.

This locking mechanism operates in somewhat the same manner as that described in connection with Fig. 1, but in Fig.k 4 the energizing circuit for the locking coil LC is controlled through a back contact 8l of the track relay TR3, so that a train, in entering the track section associated with relay TR1i is effective to quickly decrease the current in the track relay and also the coll AC, but inasmuch as the response of the plunger AP to this quickly decreased energization of coil AC is delayed by the washer 19, the track relay TRE* releases its armature before the regulator can reduce the resistance inserted into the track circuit by the variable resistor VR, and the dropping of the track relay then energizes the locking coil LC to cause the braking member 83 to prevent further actuation of the rod 69 as long as the train is occupying the associated track section.

In describing the present invention, attention has been directed to one specific embodiment thereof, without attempting to point out the various alternate or optional features of construction, or the different organizations or combinations that may be employed. For example, it is contemplated that any one of the speciiic forms different combinations which have not herein been shown or described. It is also contemplated that a greater safety in track circuit operation may be provided in the circuits shown in Fig. 3 and Fig. 4 by providing a locking means which is normally energized to permit operation of the current regulating means and from which energy is removed upon the approach and/or presence of a train to prevent operation of the regulating means, and it is considered that the manner in which the present invention could be so modied would in view of the foregoing specification be obvious to anyone skilled in the art.

In other words, the particular embodiment o1' the present invention has been selected to facilitate in the disclosure thereof, rather than to limit the number of forms which it may assume.

What I claim is:-

l. In a track circuit, in combination with an insulated section oi track, a source of electrical energy connected across one end or the insulated section, and a track relay connected across the other end of the insulated section; regulating means arranged to vary the resistance of the connections of said track relay to the track rails and thereby maintain a substantially constant current in the track relay regardless of gradual voltage changes thereacross but to permit current changes in the track relay resulting from relatively abrupt and greater voltage changes thereacross, and means retaining any condition of said regulating means while the track relay is dropped.

2. In a track circuit, in combination with an insulated section of track, a source of electrical energy connected across one end of the insulated section, and a track relay connected across the other end of the insulated section; regulating means maintaining a substantially constant current in the track relay regardless of gradual voltage changes across the insulated section by varying the resistance in the track relay connections, means delaying the response oi the current regulating means to an abrupt and re1- atively large decrease in voltage across the insulated section, and means retaining any condition of the current regulating means until the condition causing said abrupt and relatively large decrease in voltage is removed.

3. A railway signaling track circuit, having in combination, an insulated track section, a source of electrical energy connected across a iirst end of the track section, a track relay and a compressible carbon pile resistor connected in series across the second end of the track section, an electro-magnetic actuator having slower .acting characteristics than the track relay and connected in multiple with the track relay, means connecting the actuator to the carbon pile resistor whereby the carbon pile resistor is variably compressed in direct proportion to variations in voltage across the actuator, and an electro-magnetic brake operable when energized through a back contact of the track relay to prevent movement oi the means connecting the actuator to the carbon pile resistor.

i. In a railway signaling track circuit oi' the class wherein a source of electrical energy is connected across one end of an insulated track section and a relay is connected across the other end thereof to eilect the picking up or the dropping of the relay in accordance with the respective unoccupied or occupied condition of the track section by a train, the combination of a miauw current regulating means for varying the resistance in the track relay connections and thereby maintaining a substantially normal energizing current in the track relay regardless of gradual variations in inter-rail potential at the relay end ,of the track section during an unoccupied condition of the track section, and a locking means Preventing a change in condition of the current regulating means when and throughout the time in which the track section is occupied.

5. In'a railway signaling track circuit of the class wherein a source of electrical energy supplies current through an insulated section of track rails to energize a track relay, the combination of a variable resistor and a iixed resistor in series between the source of energy and the rails, an electro-magnetic actuating means connected across the track rails at the energy end of the track circuit and arranged to vary the resistance of the variable resistor in inverse proportion to gradual voltage changes in the track circuit, means for retarding the response of the actuating means to an abrupt increase in current in the track circuit, and means for preventing a change in resistance of the variable resistor by said actuating means after an abrupt and relatively large increase in current in the track circuit and as long as said increased current continues to flow therein.

6. In a railway signaling track circuit of the class wherein a source of electrical energy supplies current through an insulated section of track rails to energize a track relay, the combination of a variable resistor and a fixed resistor in series between the source of energy and the rails, an electro-magnetic actuating means arranged to vary the resistance of the variable resistor in inverse proportion to gradual increment changes in the degree oi' the energization thereof, circuit means whereby the actuating means is energized in proportion to the current through said variable and iixed resistors, means for retarding the response of the actuating means to an abrupt increase in the energization thereoi', and means for preventing a change in resistance of the variable resistor after an abrupt increase in current of a predetermined value greater than any said increment changes through said variable and fixed resistors and as long as said abrupt increase in current continues to flow therein.

7. In a railway signaling track circuit, in combination with an insulated section of track and a source of energy energizing a track relay over a circuit including the rails of the insulated section of track; automatic regulating means adjacent said track relay for maintaing a substantially constant current in the track relay regardless of gradual changes in the amount of current supplied by the source of energy, and locking means for preventing any change in condition of the regulating means when and as long as an abnormal current is supplied by the source of energy providing such abnormal current is obtained abruptly and the amount of change is above a predetermined value.

8. In a railway signaling track circuit of the class wherein a source of electrical energy supplies current through an insulated section of track rails to energize a track relay; the combination of an electro-magnetic regulator arranged to maintain a substantially constant current in the track relay regardless of gradual changes in inter-rail leakage current in the track circuit, and means actuated by the entrance of a train into an adjacent track section for rendering said regulator ine!- fective.

9. In a track circuit regulator, an insulating vertical tube, a carbon resistance rod within the vertical tube and connected in the track circuit, means emitting mercury into the lower end of the vertical tube, and an electro-magnetic means energized by the track: circuit for varying the amount of mercury emitted into the vertical tube to thereby vary the length of the resistance rod carrying track circuit current, said mercury emitting means being arranged to retard the response of the electro-magnetic means to an abrupt change in track circuit current.

10. In a track circuit current regulator, an insulating vertical tube, a carbon resistance rod within the vertical tube and connected in the track circuit, means emitting mercury into the lower end of the vertical tube, an electro-magnetic means energized by the track circuit for varying the amount of mercury emitted into the vertical tube to thereby vary the length of the resistance rod carrying track circuit current and an electromagnetic means for at times preventing emission of mercury into the vertical tube.

11. In a regulator for track circuits, two parallel insulating strips, a continuous resistance wire wound on each of the strips and included in the track circuit, an evacuated tube enclosing the strips and included in the track circuit, an evacuated tube enclosing the strips, a globule of mercury placed within the evacuated tube so as to electrically connect the resistance wire on one oi the strips to the resistance wire on the other of the strips at substantially one point only, and electro-magnetic means energized by the track circuit and moving the evacuated tube in a manner to shift the mercury globule within the tube to thereby vary the length of resistance wire carrying track circuit current, and to thereby retard the response of the electro-magnetic means to an abrupt change in track circuit energzation.

12. In a regulator for track circuits, a track circuit including rails, a battery source and a track relay, a field structure having oppositely disposed parallel plane pole faces, an armature having a horizontal core with oscillable plane vanes on the core parallel with and coasting with said pole faces, a stationary winding surrounding said core and energized by said battery source included in the track circuit, and a variable resistor in series in the track circuit and actuated by said armature.

13. In combination, a track section, a battery source for normally energizing the track section, a track relay associated with the track section, means maintaining a substantially normal current in the track relay regardless of gradual and relatively small changes in interrail potential by varying the resistance of the track relay connections, and means precluding the operation of the regulator in response to relatively large changes in interrail potential.

14. In combination, a track circuit, a track relay included in said circuit, a regulator slower acting than the track relay and arranged to maintain a substantially constant current through the track relay regardless of various weather changes, and a locking means controlled by said track relay and arranged to prevent a change in condition of the regulator whenever the track relay is dropped.

15. In combination, a track section provided with the usual closed track circuit including a normally energized track relay at one end and a track source of current at the other, a regulator for maintaining a substantially constant current in said track relay irrespective of gradual changes in interrail resistance or track source voltage changes by varying the resistance of the connections between said track relay and the track rails, and means actuated in response to a regular train movement for preventing the operation of said regulator in response to a train shunt on said track circuit.

16. In a track circuit, in combination with an insulated track section, a source of electrical energy connected across one end of the track section, and a track relay connected across the other end of the track section; a variable resistor in series with the track relay, an electro-magnetic actuator controlling the variable resistor, means energizing the actuator in accordance with the voltage across the track relay, means retarding the response of the actuator to abrupt voltage changes across the track relay, and an electromagnetic lock operating to prevent a change in condition of the variable resistor when and always when the track relay is dropped.

17. In a track circuit, in combination with an insulated track section, a source of electrical energy connected across one end of the track section, and a track relay connected across the other end of the track section; a variable resistor in series with the track relay, an electro-magnetic actuator Icontrolling the variable resistor, means energizing the actuator in accordance with the voltage across the track section, means retarding the response of the actuator to an abrupt decrease in voltage across the track section, and means preventing a change in condition of the variable resistor after an abrupt decrease in voltage across the track section and until said voltage returns substantially to its original value.

18. A railway signaling track circuit, having in combination, an insulated track section, a source of electrical energy connected across a rst end of the track section, a track relay and a variable resistor connected in series across a second end oi.' the track section, an electro-magnetic actuator having slower acting characteristics than the track relay and connected in multiple with the track relay, means connecting the actuator to the variable resistor whereby the resistance of the variable resistor is varied in direct proportion to .variations in voltage across the actuator, and an electro-magnetic brake operable when energized through a back contact of the track relay to prevent movement of the means connecting the actuator to the variable resistor.

19. In combination, a railway track circuit of the normally energized type, a track relay at one end of said track circuit and arranged to operate on a particular degree of energization, a battery source at the other end of said track circuit, a variable resistor included in series in said track circuit at the battery end, means responsive to the potential across said track circuitat the battery end to actuate said variable resistor to gradually raise or lower the resistance in said circuit so as to maintain said track relay energized above said particular degree of energization and below another particular higher degree of energization when gradual changes in potential occur within limits of said particular degree and said higher degree of energization, and means preventing actuation of said variable resistor when abrupt changes in inter-rail potential are caused by the presence of a train in the track circuit so as to -reduce the degree of energization of said track relay below said particular degree.

20. In combination; a track circuit including a section of railway track, a track relay, a battery source and a variable resistor all connected in series; regulating means responsive to gradual changes in the potential across said track to actuate said variable resistorin a manner to maintain said potential within predetermined limits while said regulating means is active; and means responding to an abrupt change in the inter-rail potential caused by the entrance of a train into the track circuit for rendering said regulating means inactive.

2l. In combination; a track circuit including a section of railway track, a track relay, a battery source and a variable resistor all connected in series; regulating means responsive to gradual changes in the potential across said track to actuate said variable resistor in a manner to maintain said potential within predetermined limits while said regulating means is active; said regulating means being relatively slow acting; and means operable more quickly than said regulating means and responding to the presence of a train in the track circuit for rendering said regulating means inactive.

22. In combination; a track circuit including a section of railway track, a track relay, a battery source and a variable resistor all connected in series; regulating means responsive to the potential across said track to actuate said variable resistor in a manner to maintain said potential within predetermined limits above the operating potential required for said track relay provided changes in potential are gradual within said limits, and means responsive to an abrupt potential change beyond said limits to render said regulating means inactive.

23. In combination; a track circuit including Aa section of track, a track relay, a source oi energy and a variable impedance all connected in series; regulating means controlled in accordance with the degree of energization of said track relay; means rendering said regulating device slower in response than said track relay to a change in the degree of energization; and means allowing said regulating means to operate said variable impedance only when said track relay is picked up.

24. In combination, a track circuit for railroads, a track relay included in said track circuit, a current regulating device in multiple with said track relay and slower in its operation than the track relay, a variable resistor controlled by said device for maintaining substantially constant current through said relay of a predetermined value above the operating value of said track relay, whereby small variations within said predetermined value are compensated for but larger variations outside of said predetermined value deenergize said track relay, and means for maintaining said device in its then existing adjusted condition while said track relay is deenergized.

25. In combination; a section of railway track, detecting means for detecting the resistance between the rails of said section including a source of current connected across the rails at one end of said section and an electro-responsive contact controlling means connected in series with said source and across the rails at the other end of said section, said detecting means including means for allowing opening of said contact due to a quick decrease in the resistance between said i'to' said quick decrease of resistance.

26. In combination; a section of railway track, detecting means for detecting the resistance between the rails of said section including a source of current connected across the rails at one end oi said section and an electro-responsive contact controlling means connected in series with said source and across the rails at the other end of said section, said detecting means including means for allowing operation of said contact due to a quick decrease in the resistance between said rails but not allowing operation of said contact due to a slow decrease of resistance between said rails; and means controlled by said contact for maintaining said detecting means in its operated condition until the resistance between said rails is again of substantially the same value as existed prior to said quick decrease of resistance.

27. In combination; a section of railway track; a source of current connected across the rails of said section at one end of said section; inter-rail resistance detecting means including an electroresponsive means having normally closed contacts and connected across the rails of said section at the other end of said section, said electroresponsive means being connected in series with said rails and said source, said detecting means including means for causing opening of said contacts upon a sudden decrease in said inter-rail resistance but allowing said contacts to remain closed if a gradual decrease in inter-rail resistance takes place; and locking means for maintaining said detecting means in its open contact condition after each sudden decrease of resistance until the inter-rail resistance is again of substantially the same value as it was prior to said sudden decrease of inter-rail resistance, whereby said contacts are open during the presence of a train in said section.

28. In combination; a section of railway track; a source of current connected across the rails of said section at one end of said section; inter-rail shunt detecting means including an electro-responsive means having normally closed contacts and connected across the rails of said section at the other end oi said section, said electro-responsive means being connected in series with said rails and said source, said detecting means including means for causing opening of said contacts upon a sudden increase in inter-rail shunt but allowing said contacts to remain closed if a gradual increase in inter-rail shunt takes place; and locking means for maintaing said detecting means in its open contact condition after each sudden increase in inter-rail shunt until the inter-rail shunt is again oi substantially the same value as it was prior to said sudden increase o! inter-rail shunt, whereby said contacts are open during the presence of a train in said section due to the suddenness of application of the train shunt but are not opened due to a gradually applied inter-rail shunt as may occur due to a change of weather conditions.

29. In combination; a section oi railway track having two spaced rails; means for supplying an electric potential across said rails at one end of said s ection; electro-responsive means at the other end of said section connected across said rails and responsive to change its condition in 1l ,ismov accordance with the inter-rail potential at that end; and holding means for preventing a change in the condition or said electro-responsive means when a relatively suddenk decrease in inter-rail potential occurs. said holding means remaining eilective until said inter-rail potential increases to the value before such sudden decrease.

30. In a. track circuit for railroads. in combination with a. source oi current and a limiting resistance connected across the track rails of a track section at one end thereof. circuit controlling means connected acroaa the track rails at the other end of said track section and including a movable element automatically assuming di!- !erent positions in accordance with gradual changes in the potential across said track rails, and means responsive to a relatively sudden decrease in the potential across the track rails for maintaining said movable element in its then existing position.

n OSCAR B. FIEID. 

